Pharmaceutical solid state · Industry updates · Page 3
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Three elusive meloxicam polymorphs required different structure-determination approaches. Single-crystal X-ray diffraction solved Form III, combined crystal structure prediction and NMR crystallography solved Form II, and electron diffraction resolved Form V, which contains four independent molecules in the asymmetric unit. The comparison highlights complementary strengths and limitations rather than establishing one universally superior crystallographic method.
3D electron diffraction resolved the structure of the ninth reported indomethacin polymorph, designated sigma, from crystals found within an amorphous solid dispersion. Subsequent experiments produced the same form by solvent evaporation. The work demonstrates structure determination directly from a formulation-related sample containing an excipient; it does not establish improved dissolution or clinical performance for the new form.
Two previously unreported piroxicam polymorphs, Forms VIII and IX, emerged through polyethylene glycol-assisted melt crystallization. Their crystal structures were determined by 3D electron diffraction. Comparing the newly solved Form VIII with known Form IV allowed discussion of how differences in intermolecular hydrogen bonding contribute to melting behavior. The study concerns laboratory solid forms rather than validated drug-product performance.
Researchers used MicroED to determine the crystal structures of ranitidine hydrochloride Forms 1 and 2. The resulting structures agreed with previously reported X-ray diffraction structures. The work presents a focused pharmaceutical proof of applicability for small-quantity or microcrystalline API samples, while retaining the need to control crystal form, hydration, and residual solvents through complementary quality assessments.
Researchers determined two polymorphic crystal structures of the oral macrocyclic drug paritaprevir within the same MicroED experiment. The forms differed in macrocycle and substituent conformations. Docking suggested that one conformation could fit the viral protease binding pocket. The structural and computational results inform conformational analysis but do not establish a difference in clinical performance between polymorphs.
An automated low-dose 3D electron diffraction workflow identified six phases in a melt-crystallized griseofulvin–polyethylene glycol system. More than 230 datasets were collected and processed in three days. The researchers resolved known drug polymorphs and inclusion complexes alongside an elusive new inclusion-complex phase, then related the two inclusion-complex polymorphs to their structural stability differences.
MicroED analysis of mirabegron nanocrystals revealed two molecular conformers within the asymmetric unit and a hydrogen-bonded packing arrangement. The authors compared these solid-state conformations with a previously reported receptor-bound model and discussed differences. The two conformers are not, by themselves, evidence of two separate polymorphs; the study concerns molecular conformation within the observed crystal structure.
The authors combined liquid-assisted grinding with MicroED to characterize olanzapine molecular salts that had resisted suitable single-crystal growth. The approach also identified minor impurity structures within bulk solids. This pharmaceutical example links mechanochemical preparation to structure determination, while showing that crystallinity alone does not guarantee success with conventional single-crystal X-ray analysis.
The crystal structure of levocetirizine dihydrochloride was determined by 3D ED/MicroED from crystalline powder extracted from commercially available tablets. Dynamical refinement also supported its absolute configuration. The study provides an example of identifying and characterizing an API within a microcrystalline mixture, without requiring the growth of large single crystals or implying that every formulated product is equally accessible.
This study combined virtual screening of chiral probes, experimental cocrystal screening, and MicroED structure determination to assign absolute configuration for two marketed API molecules. Known probe stereochemistry anchors the assignment. The workflow offers a route around difficult large-crystal growth while retaining an experimental screening step; computational propensity predictions alone do not establish absolute configuration.
Researchers determined the structures of five vemurafenib polymorphs directly from compact spherulites using 3D electron diffraction. Three matched known single-crystal X-ray structures, while the method resolved a difficult delta form and a newly observed epsilon form. The work expands access to melt-grown polymorphs whose morphology or instability can frustrate conventional single-crystal analysis.
MicroED determined a powder-derived cocrystal of 2-aminopyrimidine and succinic acid prepared by solid-state grinding. The mechanically generated phase was not accessible through the solution-crystallization route examined. This is a model organic cocrystal rather than an API efficacy study, illustrating how electron diffraction can characterize crystal-engineering products without first recreating them as large solution-grown crystals.
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